The present invention concerns a phase-comparison circuit for use in the circuit system described in co-pending U.S. application Ser. No. 771,903, relating to a circuit system for a television receiver, said circuit system operating to replace a changing quadrant of the picture of a first transmitted television program with an equivalent-size sector of a second transmitted program.
Prior art television receivers in which more than one program can be viewed simultaneously have been constructed with an additional smaller television screen being placed adjacently to the main screen. However, the method of construction is very expensive because it requires a complete duplication of parts, including the television picture tube.
A method for the elimination of the additional television tube has been accomplished in television broadcast studios where the co-joining or mixing of at least one part of an additional television picture into a blanked sector of the main picture is common practice. However, the method of combining a plurality of television images taken by different in-station television cameras and reproduced together on the same receiver screen is simplified by the fact that the deflection signals for the different television camera tubes have identical timing. Thus, the described method is limited to television studio systems operating under closed-circuit conditions. The same limitation also applies to known methods for the simultaneous showing of several video signals originating from different in-station television cameras in which different saw-tooth signals are applied to the different television cameras, but where the frequencies of the signals are related to each other by integral fraction.
The simultaneous reproduction of television picture signals beamed by various television stations onto one television receiver screen has been accomplished by the blending of a reduced image of a second program into the televised picture of the main program. However, the method requires memory capability for the purpose of reducing the size of the picture of the second program and for the purpose of overcoming the difference in time between the synchronizing signals broadcast by the two stations. The size reduction of the picture of the second program has been achieved by designing the output speed for the memory to be greater than the input speed and by limiting reproduction to only every fourteenth line of the second program. The reduced picture consequently has a diminished resolution in the vertical direction.